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SEMI F73-1102 © SEMI 2002 2 4 Referenced Standards 4.1 ASTM Stan dards 1 ASTM E 7 — Standard Terminology Relati ng to Metallograp hy ASTM E 766 — Standard Practice for Calibrating the Magnificatio n of a Scanni ng Electr…

SEMI F73-1102 © SEMI 2002 1

SEMI F73-1102

TEST METHOD FOR SCANNING ELECTRON MICROSCOPY (SEM)

EVALUATION OF WETTED SURFACE CONDITION OF STAINLESS

STEEL COMPONENTS

This test method was technically approved by the Global Gases Committee and is the direct responsibility of

the North American Gases Committee. Current edition approved by the North American Regional Standards

Committee on August 29, 2002. Initially available at www.semi.org September 2002; to be published

November 2002.

1 Purpose

1.1 This document defines a uniform procedure for

testing the wetted surfaces of stainless steel components

intended for installation into high purity gas distribution

systems. This procedure characterizes the occurrence,

frequency, and in some cases the identity of

microscopic surface defects and contaminants that may

appear on the wetted surfaces. It should be noted that

there has been no direct correlation made between the

results of this test method and contamination of process

gases or product yields in processes served by high

purity gas distribution systems. Application of this test

method is intended to yield comparable and

reproducible results among various users of this method

for the purposes of qualification of components.

1.2 The objective of this method is to describe a

general set of instrument parameters and conditions that

will achieve precise and reproducible measurements of

important parameters regarding the surface condition.

2 Scope

2.1 This procedure applies to the wetted surfaces in

stainless steel tubing, fittings, valves, and other

components to determine the effectiveness of surface

finishing and cleaning processes. The technique

describes counting of surface defects including pits,

inclusions, inclusion stringers, scratches, residual

process marks, grain boundaries and contamination on

the wetted surfaces. However, any surface damage

produced during sample preparation is to be excluded

from such assessment.

2.2 This standard does not purport to address safety

issues, if any, associated with its use. It is the

responsibility of the users of this standard to establish

appropriate safety health practices and determine the

applicability or regulatory limitations prior to use.

3 Limitations

3.1 This test method is primarily intended to determine

the frequency of occurrence (surface density) and

identity of microscopic surface defects, down to a size

range of ≥ approximately 0.1 micrometer, that may be

detrimental to high purity gas distribution systems.

Such defects may not be identifiable by visual or

magnified optical inspection, but concentrations of

microscopic surface defects may cause visually

apparent defects such as haze.

3.2 This test method requires sectioning of the

specimen(s) used for test purposes and is therefore

destructive.

3.3 The method must be applied to representative

examples of process lots to determine quality of the

processes employed and/or lots processed. As the areas

examined and measured by this method are very small,

the results may not be representative of all areas or all

lots processed.

3.4 This test method may be subject to operator bias in

selection of representative areas and definition of

countable defects.

3.5 Detection of countable defects is affected by

operator selection of SEM operating conditions and

image recording conditions. This test method assumes

that the operator is sufficiently proficient in operation

of the SEM to minimize this limitation, per instructions

in the procedures.

3.6 SEM imaging will reveal surface finish flaws, but

may not show features that are well rounded by an

electropolishing or other surface leveling process.

3.7 Energy dispersive X-ray spectroscopy (EDS) may

be used in this test method to analyze surface

contaminants at least approximately one micrometer in

thickness and inclusions at least approximately one

micrometer in size. EDS is not an appropriate

technique for analysis of the oxide passive layer on the

stainless steel surface, as EDS analyzes down to a depth

of the order of 1 micrometer below the surface, and the

oxide passive layer is only 0.001 to 0.01 micrometer

deep.

SEMI F73-1102 © SEMI 2002 2

4 Referenced Standards

4.1 ASTM Standards

ASTM E 7 — Standard Terminology Relating to

Metallography

ASTM E 766 — Standard Practice for Calibrating the

Magnification of a Scanning Electron Microscope

4.2 ANSI

/IEEE Standard

759 —Standard Test Procedures for Semiconductor X-

ray Energy Spectrometers

NOTE 1: Unless otherwise indicated, all documents cited

shall be the latest published versions.

5 Terminology

5.1 Abbreviations and Acronyms

5.1.1 EDS — Energy Dispersive X-ray spectroscopy,

sometimes called EDX.

5.1.2 FWHM — abbreviation of Full Width Half

Maximum; the width of an EDS peak measured at half

its maximum height.

5.1.3 SEM — Scanning Electron Microscopy.

5.2 Definitions

5.2.1 defect — any surface feature that is either

characteristic of the material, or a result of material

processing or product fabrication, that is deemed

capable of generating and/or trapping and releasing

particles, or otherwise be detrimental to the contained

fluids. Specific features that may be considered to be

defects, with definitions that relate to the purposes of

this document and/or obtained from reference sources

noted include:

5.2.1.1 contamination — three dimensional alien

material adhering to a surface. (SEMI Compilation of

Terms)

5.2.1.2 grain boundary — an interface separating two

grains, where the orientation of the lattice changes from

that of one grain to that of the other. (ASTM E 7)

5.2.1.3 inclusion — indigenous or foreign material

within the metal, usually referring to non-metallic

1 American Society for Testing and Materials, 100 Barr Harbor

Drive, West Conshohocken, Pennsylvania 19428-2959, USA.

Telephone: 610.832.9585, Fax: 610.832.9555 Website:

www.astm.org

2 American National Standards Institute, New York Office: 11 West

42nd Street, New York, NY 10036, USA. Telephone: 212.642.4900;

Fax: 212.398.0023 Website: www.ansi.org

3 Institute of Electrical and Electronics Engineers, IEEE Operations

Center, 445 Hoes Lane, P.O. Box 1331, Piscataway, New Jersey

08855-1331, USA. Telephone: 732.981.0060; Fax: 732.981.1721

compound particles such as oxides, alumina, sulfides or

silicates.

5.2.1.4 pit — a surface cavity or crater with a defined

edge not caused by impact.

5.2.1.5 process marks — a surface texture or pattern

that is characteristic of the surface finishing process

employed.

5.2.1.6 scratch — an elongated mark or groove cut in

the surface by mechanical means, not associated with

the predominant surface texture pattern. (adapted from

SEMI Compilation of Terms)

5.2.1.7 stringer — a microstructural configuration of

alloy constituents or foreign nonmetallic material, or

trace thereof, lined up in the direction of working.

(adapted from ASTM E 7)

5.2.2 wetted surface — surfaces of a component

contacting the contained fluids. (adapted from SEMI

Compilation of Terms)

5.2.3 working distance — the distance between the

surface of the specimen being examined and the front

surface of the objective lens. (ASTM E 7)

6 Summary of Method

6.1 Obtain a SEM photomicrograph of a representative

area of the wetted surface of the sample at a

magnification of 200×. Increase the magnification to

1000× and take another SEM photomicrograph within

this area, and another at a pre-selected magnification

within the range 3000 to 3600×. Obtain 3000–3600×

photomicrographs at two additional representative

areas, not necessarily within the 200× magnification

region.

6.2 If inclusions or contaminants are noted on any

3000–3600× magnification photos, EDS spectra of

representative example(s) may be obtained.

6.3 Perform grid overlay defect counting on the three

3000–3600× photos. Report results in tabular form;

provide photomicrographs and EDS spectra with

identification of elements detected.

7 Interferences

7.1 Interferences may be encountered as overlaps in

EDS spectral peaks. Specific overlaps that may be

encountered include but are not limited to:

7.1.1 Molybdenum and Sulfur — Overlap in EDS

spectra of Mo L peaks and S K peaks prevents

unambiguous determination.

7.1.2 Manganese and Chromium/Iron — Overlap in

EDS spectra of Mn Kα peak with Cr Kβ peak, and Mn

SEMI F73-1102 © SEMI 2002 3

Kβ peak with Fe Kα peak interferes with determination

of low levels of Manganese in Iron-Chromium matrix.

8 Apparatus

8.1 Instrumentation — Any SEM instrument used for

this method must be capable of a minimum point-to-

point resolution of 30 nm, as measured with a NIST

traceable standard. Any commercially available SEM

with image recording capabilities of at least 100 cm

image and an EDS analyzer capable of 170 eV or less

FWHM resolution for Mn Kα may be employed.

8.2 The SEM shall have a sample stage capable of

aligning the sample to provide multiple areas of view

with the orientation of the electron beam approximately

normal to the surface, and to optimize secondary

electron and X-ray signal collection efficiencies.

8.3 Grid Overlay — A transparent grid overlay of grid

size equal to 1.814 micrometers multiplied by the pre-

selected magnification in the range 3000 to 3600 (grid

size would be 6.35 mm [= ¼ inch] square for 3500×

magnification). The grid lines shall be as fine as

possible but clearly visible. The grid overlay shall be

designed to overlay the image of a photomicrograph

with 252 grids (18 by 14 grids for the 3.5 by 4.5 inch

image of a standard Polaroid photomicrograph) with

minimal interference from alphanumeric information

recorded with the photomicrograph, but without

reference to any features in the photomicrograph. The

rows and columns of the grid overlay may be indexed

with alphanumerics to identify and locate specific

features in the photomicrographs (see examples in

Appendices 1 and 2). It is suggested that a fixed

reference point for the edges of the photomicrograph be

established to be consistently used in all overlays.

9 Reagents and Materials

9.1 Sample Preparation Materials — Equipment

required to section the test specimen without damaging

or contaminating the surfaces to be analyzed. A clean,

dry hacksaw or dry bandsaw is recommended, using a

slow cutting speed to avoid excessive sample heating.

9.2 Sample Mounting Materials — Sample mounting

holders specific to the SEM instrument used.

Conductive paste or tape used to adhere the sample to

the holder must be vacuum stable and applied so that

the area of analytical interest is not contaminated.

10 Safety Precautions

4 National Institute of Standards and Technology, 100 Bureau Drive,

Stop 3460,Gaithersburg, MD 20899, (301) 975-NIST (6478) TTY (301)

975-8295, website: www.nist.gov.

10.1 This test method does not purport to address the

safety considerations associated with use of high

voltage, vacuum, electron and X-ray producing

equipment.

10.2 The method assumes a SEM and EDS analyst

with adequate skill level as well as knowledge of

instrumentation and associated safety precautions.

11 Test Specimen

11.1 Specimens are to be sectioned to appropriate size

for the particular SEM instrument. Any sample

preparation technique used shall avoid introducing

contamination onto the surface to be measured. In

addition, preparation must avoid heating of the sample

in excess of approximately 100°C to avoid oxide

growth or change in surface composition. Slow speed

dry cutting is recommended.

11.2 After preparation, samples shall be protected from

contamination by means such as sealing in

noncontaminating bags or wrapping in clean aluminum

foil. Appropriate cleaning of the analysis surface to

remove sample preparation residues is allowed but not

required. Any such cleaning procedures should be

stated in the report. After sectioning, samples should

be analyzed promptly.

11.3 The samples shall be analyzed in the uncoated

condition; ie, without sputtering with a conductive

coating.

12 Preparation of Apparatus

12.1 The SEM shall be in good condition to assure

proper performance in accordance with the

manufacturer’s specifications.

13 Calibration and Standardization

13.1 Instrument calibration for magnification and EDS

performance shall be performed in accordance with

ASTM E 766 and ANSI-IEEE 759 and/or the

instrument manufacturer’s recommendations. The

magnification should be calibrated at the working

distance selected. Calibration frequency shall be per

instrument manufacturer’s recommendations.

14 Procedure

14.1 The sample is to be mounted in accordance with

manufacturer' s recommendations and in a manner

consistent with high vacuum analytical procedures. The

sample shall be oriented such that the areas of interest

for SEM imaging can be viewed at 70 to 90° incidence

angle of the electron beam to the surface with optimum

secondary electron collection efficiency, and the ability

to re-orient the sample for optimization of X-ray